Breathing Spots in a Reaction-Diffusion System

A quasi-2-dimensional stationary spot in a disk-shaped chemical reactor is observed to bifurcate to an oscillating spot when a control parameter is increased beyond a critical value. Further increase of the control parameter leads to the collapse and disappearance of the spot. Analysis of a bistable activator-inhibitor model indicates that the observed behavior is a consequence of interaction of the front with the boundary near a parity breaking front bifurcation.Comment: 4 pages RevTeX, see also http://chaos.ph.utexas.edu/ and http://t7.lanl.gov/People/Aric

Diffusion with rearranging traps

A model for diffusion on a cubic lattice with a random distribution of traps is developed. The traps are redistributed at certain time intervals. Such models are useful for describing systems showing dynamic disorder, such as ion-conducting polymers. In the present model the traps are infinite, unlike an earlier version with finite traps, this model has a percolation threshold. For the infinite trap version a simple analytical calculation is possible and the results agree qualitatively with simulation.Comment: Latex, five figure

Multishank Thin-Film Neural Probes and Implantation System for High-Resolution Neural Recording Applications

Abstract Silicon probes have played a key role in studying the brain. However, the stark mechanical mismatch between these probes and the brain leads to chronic damage in the surrounding neural tissue, limiting their application in research and clinical translation. Mechanically flexible probes made of thin plastic shanks offer an attractive tissue‐compatible alternative but are difficult to implant into the brain. They also struggle to achieve the electrode density and layout necessary for the high‐resolution applications their silicon counterparts excel at. Here, a multishank high‐density flexible neural probe design is presented, which emulates the functionality of stiff silicon arrays for recording from neural population across multiple sites within a given region. The flexible probe is accompanied by a detachable 3D printed implanter, which delivers the probe by means of hydrophobic‐coated shuttles. The shuttles can then be retracted with minimal movement and the implanter houses the electronics necessary for in vivo recording applications. Validation of the probes through extracellular recordings from multiple brain regions and histological evidence of minimal foreign body response opens the path to long‐term chronic monitoring of neural ensembles

Breathing Current Domains in Globally Coupled Electrochemical Systems: A Comparison with a Semiconductor Model

Spatio-temporal bifurcations and complex dynamics in globally coupled intrinsically bistable electrochemical systems with an S-shaped current-voltage characteristic under galvanostatic control are studied theoretically on a one-dimensional domain. The results are compared with the dynamics and the bifurcation scenarios occurring in a closely related model which describes pattern formation in semiconductors. Under galvanostatic control both systems are unstable with respect to the formation of stationary large amplitude current domains. The current domains as well as the homogeneous steady state exhibit oscillatory instabilities for slow dynamics of the potential drop across the double layer, or across the semiconductor device, respectively. The interplay of the different instabilities leads to complex spatio-temporal behavior. We find breathing current domains and chaotic spatio-temporal dynamics in the electrochemical system. Comparing these findings with the results obtained earlier for the semiconductor system, we outline bifurcation scenarios leading to complex dynamics in globally coupled bistable systems with subcritical spatial bifurcations.Comment: 13 pages, 11 figures, 70 references, RevTex4 accepted by PRE http://pre.aps.or

<span style="font-size:10.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language: HI" lang="EN-US">Relaxation phenomena of acrylic esters and phenols in dilute solution of CCl₄ under static and high frequency electric field</span>

725-735Double relaxation times 2 and 1 due to whole molecular rotation and the flexible parts of the binary (jk) polar mixture of p-cresol, p-chlorophenol, 2,4 dichlorophenol and p-bromophenol with methyl methacrylate (MMA) or ethyl methacrylate (EMA) were estimated under 9.37 GHZ electric field dissolved in dilute CCl4 solution at 35°C using high frequency susceptibility data ijk’s for different weight fractions wjk’s. Six systems out of eight exhibit 2, 1; c2, c1 and μ2, μ1, respectively. The estimated 2’s and μ2’s agree well with the measured and reported values indicating the whole rotation of binary polar mixture under high frequency electric field. Solute-solute and solute-solvent molecular formation through H-bonding are ascertained from μav – xj curves for 0.5 mole fraction xj of acrylic ester. The associational aspects are taken into consideration in μtheo from the stand point of inductive, mesomeric and electromeric effects within the polar groups of the molecules. Static μ0’s are calculated and compared with the reported values also

Dielectric behaviour of aprotic polar liquid dissolved in non-polar solvent under static and high frequency electric field

175-183Dielectric behaviour of aprotic polar liquids (j) like N,N dimethylformamide (DMF), N,N dimethylacetamide (DMA) and acetone (Ac) has been studied under static as well as 9.987, 9.88 and 9.174 GHz electric field employing Debye theory of polar-non polar liquid mixture in terms of measured ε'ij and imaginary ε"ij part of complex relative permittivity εij*, static ε0ij and high frequency ε∞ij for different wj’s of solute dissolved in non polar solvent at 27°C temperature. Double relaxation times τ2 and τ1 due to whole molecule and part of the polar molecule have also been estimated analytically using the complex high frequency orientational susceptibility ij* (= εij*-ε∞ij) from measured data for DMF and DMA in C6H6 and CCl4 as well as acetone in C6H6 and CCl4 solvent, respectively at 27°C. Out of the six systems, three systems show double relaxation time τ2 and τ1 and dipole moment μ2 and μ1. The estimated μ’s and τ’s agree excellently well with the reported and measured values from ratio of slope and linear slope method. The dipole moments μ0s’s in static electric field are also compared with μj’s in hf method. The relative contributions c1 and c2 due to τ1 and τ2 have been calculated from Fröhlich equation as well as graphical plot of 'ij/0ij -wj and ''ij/0ij -wj curve at wj→0. Solute-solute and solute-solvent molecular associations are ascertained in different molecular environment

Effective medium theory for ionic conductivity in polycrystalline solid electrolytes

It is usually found that for the relatively poor ion conducting solids, the ionic conductivity for the pure polycrystalline sample is higher than that of the single crystal. The difference has been suggested to be due to the presence of dislocations grain boundaries etc. in the polycrystal. In this paper we propose a theoretical model for the polycrystal including these defects. A quantitative estimate of the grain boundary contribution to conductivity is made using an effective medium theory and it is found to exhibit an Arrhenius behaviour. The results for calcium fluoride, thallium chloride and cuprous chloride show that the grain boundary conductivity is &#8776; 105 times that of the single crystal. The ratio of activation energy for grain boundary conduction to that of the single crystal is found to be 0.5–0.6 which is consistent with results obtained from other sources

Ionic conductivity of PEO-NH₄ClO₄ films by admittance spectroscopy: correlation with crystallinity and morphology

In this paper we present a study of ionic conductivity versus salt fraction for PEO-NH₄ClO₄ films. Films with salt concentration x in the range 0 – 0.35 (x is the weight fraction of the salt) were prepared for the study. X-ray diffraction and differential scanning calorimetry were done to detect the different species present and to estimate the crystallinity of the films. The films have a wide variety of structures and exhibit a transformation from fractal to nonfractal morphology as x is increased. We attempt a correlation of ionic conductivity with crystallinity and morphology of films with varying x and find that the fractal to compact crossover region has the highest ionic conductivity

A COMPUTER SIMULATION STUDY OF IONIC CONDUCTIVITY IN POLYMER ELECTROLYTES

simulation In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganisation of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH4I and PEO-NH4SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.

Thermal diffusivity of advanced composite materials of e-glass fiber reinforced plastic in the temperature range 5-120K

273-276Thermal diffusivity of plain-woven fabric composite in a closed cycle cryo-refrigerator (CCR) based setup in the temperature range 5-120K has been studied. The modified temperature wave method (Angstrom) is applied to measure the thermal diffusivity of glass fiber reinforced plastic (GFRP). The set up is a plug in type which can be used anywhere because of its portability and also works without use of any cryogenic fluid. The results show that there exists an inverse relation between the thermal diffusivity of e-glass fiber composite and temperature in very low temperature domain but decreases very slowly after 100K